Semiconductor device and display device

ABSTRACT

An increase in fabricating cost of a display module including a touch sensor is suppressed. A display device which includes a first substrate, a second substrate, and liquid crystal interposed between the first substrate and the second substrate includes a display portion. The display portion includes a sensor unit and a pixel. The sensor unit includes a first transistor, a first conductive film electrically connected to a gate of the first transistor, and a second conductive film. At least part of the first conductive film overlaps with at least part of the second conductive film. The pixel includes a second transistor, and a pixel electrode electrically connected to the second transistor. At least part of the pixel electrode overlaps with at least part of the first conductive film.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a touch sensor.Another embodiment of the present invention relates to a display deviceincluding a touch sensor or a display panel, or a touch sensor and adisplay panel in combination.

Note that the term “display panel” in this specification and the likemeans all display devices such as a liquid crystal panel, an organic ELpanel, and an inorganic EL panel. The term “semiconductor device” meansall devices which can operate by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an electro-optical device, and an electronic device may have asemiconductor device. In addition, a display device including a touchsensor and a display panel is referred to as a display module in somecases.

Note that one embodiment of the present invention is not limited to theabove technical field. One embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or afabricating method. One embodiment of the present invention relates to aprocess, a machine, manufacture, or a composition of matter. Thus, morespecific examples of the technical field of one embodiment of thepresent invention disclosed in this specification include asemiconductor device, a display device, a light-emitting device, anelectronic device, an input device, an input/output device, a method fordriving any of them, and a method for fabricating any of them.

2. Description of the Related Art

As a flat panel display, a display device including a liquid crystal isknown. An electronic device in which the display device is used for adisplay portion is known. Such an electronic device includes an inputportion used for operating the electronic device, for example.

A touch sensor is known as an example of the input portion. Anelectronic device including a touch sensor overlapping with a displaypanel, in which display images can be changed by an input with the useof the touch sensor, has been desired. In the touch sensor, a capacitivetouch technology, a resistive touch technology, an optical touchtechnology, and the like are known as its method for detecting an inputsignal.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. H09-281508

SUMMARY OF THE INVENTION

When a display module including a touch sensor is fabricated, a surfaceof a display portion included in a display panel for displaying imagesis apart from a detection surface of a touch sensor for detecting inputsignals because a touch panel is provided over a display panel with anadhesive layer interposed therebetween. Thus, some problems arise inthat input is not smoothly performed, for example. Specifically, whenthe display surface is seen diagonally through a touch sensor, iconsdisplayed on the display surface deviate from the sensing positions ofthe touch panel, which inhibits an accurate input.

In view of the above technical background, an object of one embodimentof the present invention is to provide a display module including atouch sensor in which wrong input can be reduced. Another object of oneembodiment of the present invention is to improve the reliability of adisplay module including a touch sensor.

When a display module including a touch sensor is fabricated, a touchsensor overlaps with a display panel, which makes it difficult to reducethe thickness. An object of one embodiment of the present invention isto reduce the thickness of a display module including a touch sensor.Another object of one embodiment of the present invention is to reducethe weight of a display module including a touch sensor.

When a display module including a touch sensor is fabricated, a touchsensor and a display panel are fabricated separately and then need to becombined with each other, which leads to an increase in fabricatingcost. An object of one embodiment of the present invention is to preventan increase in fabricating cost of a display module including a touchsensor.

Another object of one embodiment of the present invention is to providea novel structure of a display module including a touch sensor. Anotherobject of one embodiment of the present invention is to provide a noveltouch sensor. Another object of one embodiment of the present inventionis to provide a novel display. Another object of one embodiment of thepresent invention is to provide a novel display module.

Note that the descriptions of these objects do not disturb the existenceof other objects. One embodiment of the present invention does notnecessarily solve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

In one embodiment of the present invention, a display device whichincludes a first substrate, a second substrate, and liquid crystalinterposed between the first substrate and the second substrate includesa display portion. The display portion includes a sensor unit and apixel. The sensor unit includes a first transistor, a first conductivefilm electrically connected to a gate of the first transistor, and asecond conductive film. At least part of the first conductive filmoverlaps with at least part of the second conductive film. The pixelincludes a second transistor, and a pixel electrode electricallyconnected to the second transistor. At least part of the pixel electrodeoverlaps with at least part of the first conductive film.

In another embodiment of the present invention, a display device whichincludes a first substrate, a second substrate, and liquid crystalinterposed between the first substrate and the second substrate includesa display portion. The display portion includes a sensor unit and apixel. The sensor unit includes a first transistor, a first conductivefilm electrically connected to a gate of the first transistor, and asecond conductive film. The first transistor and the first conductivefilm are provided between the first substrate and the liquid crystal.The second conductive film is provided so as to face the firstconductive film with the first substrate interposed therebetween. Atleast part of the first conductive film overlaps with at least part ofthe second conductive film. The pixel includes a second transistor, anda pixel electrode electrically connected to the second transistor. Atleast part of the pixel electrode overlaps with at least part of thefirst conductive film.

In another embodiment of the present invention, a display device whichincludes a first substrate, a second substrate, and liquid crystalinterposed between the first substrate and the second substrate includesa display portion. The display portion includes a sensor unit and apixel. The sensor unit includes a first transistor, a first conductivefilm electrically connected to a gate of the first transistor, and asecond conductive film. The first transistor and the first conductivefilm are provided between the first substrate and the liquid crystal.The second conductive film is provided so as to face the firstconductive film with the liquid crystal interposed therebetween. Atleast part of the first conductive film overlaps with at least part ofthe second conductive film. The pixel includes a second transistor, anda pixel electrode electrically connected to the second transistor. Atleast part of the pixel electrode overlaps with at least part of thefirst conductive film.

In another embodiment of the present invention, a display device whichincludes a first substrate, a second substrate, and liquid crystalinterposed between the first substrate and the second substrate includesa display portion. The display portion includes a sensor unit and apixel. The sensor unit includes a first transistor, a first conductivefilm electrically connected to a gate of the first transistor, and asecond conductive film. At least part of the first conductive film isadjacent to at least part of the second conductive film. The pixelincludes a second transistor, and a pixel electrode electricallyconnected to the second transistor. At least part of the pixel electrodeoverlaps with at least part of the first conductive film.

In the above, the first transistor is preferably formed in the samefabrication process at the same time as the second transistor.

According to one embodiment of the present invention, a sensor unit canbe formed at the same time as a pixel, which can reduce fabricating costof a display device integrated with a sensor. The thickness of a displaydevice integrated with a sensor can be reduced. The weight of a displaydevice integrated with a sensor can be reduced. The thickness and weightof a display device integrated with an active matrix sensor can bereduced. A highly reliable display device integrated with a sensor whosedetection sensitivity is improved can be provided. According to anotherembodiment of the present invention, a novel structure of a displaymodule including a touch sensor can be provided. Another embodiment ofthe present invention can provide a novel touch sensor. Anotherembodiment of the present invention can provide a novel display. Anotherembodiment of the present invention can provide a novel display module.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects. Other effects will be apparentfrom and can be derived from the description of the specification, thedrawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate structure examples of a display device;

FIG. 2 illustrates a structure example of a display device;

FIG. 3 illustrates a structure example of a display device;

FIGS. 4A and 4B illustrate examples of driving methods;

FIGS. 5A and 5B illustrate examples of driving methods;

FIG. 6 illustrates a structure example of a circuit;

FIG. 7 illustrates an example of driving method;

FIG. 8 illustrates a structure example of a circuit;

FIG. 9 illustrates a structure example of a circuit;

FIG. 10 illustrates a structure example of a display device;

FIG. 11 illustrates a structure example of a circuit;

FIG. 12 illustrates a structure example of a circuit;

FIGS. 13A to 13D are Cs-corrected high-resolution TEM images of a crosssection of a CAAC-OS and a cross-sectional schematic view of a CAAC-OS;

FIGS. 14A to 14D are Cs-corrected high-resolution TEM images of a planeof a CAAC-OS;

FIGS. 15A to 15C show structural analysis of a CAAC-OS and a singlecrystal oxide semiconductor by XRD;

FIGS. 16A and 16B show electron diffraction patterns of a CAAC-OS;

FIG. 17 shows a change of crystal parts of an In—Ga—Zn oxide owing toelectron irradiation;

FIGS. 18A to 18F each illustrate an example of an electronic appliance;

FIG. 19 illustrates a structure example of a display device; and

FIG. 20 illustrates a structure example of a display device.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail. Note that the present invention is not limited to thedescription below, and it is easily understood by those skilled in theart that a variety of changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention is not construed as being limited to thedescription of the embodiments given below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Further, the same hatching pattern is appliedto portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thefilm thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such a scale.

Note that in this specification and the like, ordinal numbers such as“first,” “second,” and the like are used in order to avoid confusionamong components and do not limit the number.

A transistor is a kind of semiconductor elements and can achieveamplification of current or voltage, switching operation for controllingconduction or non-conduction, or the like. A transistor in thisspecification includes an insulated-gate field effect transistor (IGFET)and a thin film transistor (TFT).

A “source” of a transistor means a source region that is part of asemiconductor film or a source electrode connected to the semiconductorfilm. Similarly, a “drain” of the transistor means a drain region thatis part of the semiconductor film or a drain electrode connected to thesemiconductor film. A “gate” means a gate electrode.

The terms “source” and “drain” of a transistor interchange with eachother depending on the conductivity type of the transistor or levels ofpotentials applied to terminals. In general, in an n-channel transistor,a terminal to which a lower potential is applied is called a source, anda terminal to which a higher potential is applied is called a drain.Further, in a p-channel transistor, a terminal to which a lowerpotential is applied is called a drain, and a terminal to which a higherpotential is applied is called a source. In this specification, althoughconnection relation of the transistor is described assuming that thesource and the drain are fixed in some cases for convenience, actually,the names of the source and the drain interchange with each otherdepending on the relation of the potentials.

In addition, even when different components are connected to each otherin a circuit diagram, there is actually a case where one conductive filmhas functions of a plurality of components such as a case where part ofa wiring serves as an electrode. The term “connection” also means such acase where one conductive film has functions of a plurality ofcomponents.

Embodiment 1

In this embodiment, a touch sensor and a liquid crystal display deviceintegrated with a touch sensor, of one embodiment of the presentinvention, are described (FIGS. 1A and 1B).

FIG. 1A illustrates a schematic view of a display device integrated withan active matrix touch sensor of one embodiment of the presentinvention. A display device 10 integrated with an active matrix touchsensor of one embodiment of the present invention includes a displayregion 100, a gate line 104 provided in the display region 100, a gateline driver circuit 20 electrically connected to the gate line 104, asource line 105 provided in the display region 100, a source line drivercircuit 30 electrically connected to the source line 105, a bus line 102provided in the display region 100, a sensor unit driver circuit 40 forthe active matrix touch sensor electrically connected to the bus line102, a bus line 103 provided in the display region 100, a conversioncircuit 50 for the active matrix touch sensor electrically connected tothe bus line 103. The display device 10 includes a flexible printedcircuit (FPC) 60.

A chip on glass (COG) method may be used as a method for mounting thesensor unit driver circuit 40, the conversion circuit 50, and the sourceline driver circuit 30. The sensor unit driver circuit 40, theconversion circuit 50, and the source line driver circuit 30 may beformed on one IC chip or formed on respective IC chips. All or part ofthe sensor unit driver circuit 40 may be formed over the display device10 using a thin film transistor. All or part of the conversion circuit50 may be formed over the display device 10 using a thin filmtransistor. All or part of the source line driver circuit 30 may beformed over the display device 10 using a thin film transistor.

FIG. 1B illustrates a schematic view of the display region 100 of thedisplay device integrated with an active matrix touch sensor. Thedisplay region 100 includes at least the active matrix touch sensor, thegate line 104, the source line 105, a transistor 106, and a pixelelectrode 107. A gate of the transistor 106 is electrically connected tothe gate line 104. One of a source and a drain of the transistor 106 iselectrically connected to the source line 105. The other of the sourceand the drain of the transistor 106 is electrically connected to thepixel electrode 107. The active matrix touch sensor includes the busline 102, the bus line 103, and a sensor unit 101. The bus line 102 iselectrically connected to the sensor unit 101. The bus line 103 iselectrically connected to the sensor unit 101. Examples of the bus line102 include a wiring VRES, a wiring RES, a scanning line GL (k), awiring CS, a wiring VPI (see FIG. 6 ). Examples of the bus line 103include a signal line DL (n) (see FIG. 6 ).

The active matrix touch sensor of one embodiment of the presentinvention includes the sensor unit 101. The sensor unit 101 includes afirst transistor and a first capacitor. The first capacitor includes afirst electrode, a second electrode, and a dielectric providedtherebetween, for example. At least part of the second electrode of thefirst capacitor overlaps with part of a pixel electrode. A transistorwhich can be formed over the first substrate at the same time as whenthe transistor 106 is formed can be used as the first transistor. Thefirst transistor and the transistor 106 are formed over the firstsubstrate, which can simplify the process for fabricating the touchpanel and reduce the fabricating cost.

FIG. 2 is a cross-sectional view of a liquid crystal display deviceintegrated with an active matrix touch sensor of one embodiment of thepresent invention. In FIG. 2 , a cross section a-a′ illustrates part ofa display element; b-b′, part of a sensor unit; and c-c′, part of acircuit.

The liquid crystal display device integrated with an active matrix touchsensor of one embodiment of the present invention includes conductivefilms 202, 203, 204, and 205 over a substrate 201. The conductive films202, 203, and 205 each function as a gate electrode of a transistor. Aninsulating film 206 is provided over the conductive films 202, 203, 204,and 205. Part of the insulating film 206 can function as a gateinsulating film of the transistor. Semiconductor films 207, 208, and 209are provided over the insulating film 206. Conductive films 210 and 211are provided over the semiconductor film 207. Conductive films 212 and213 are provided over the semiconductor film 208. Conductive films 214and 215 are provided over the semiconductor film 209. The conductivefilms 210, 211, 212, 213, 214, and 215 each can function as a source ora drain of a transistor. Insulating films 216, 217, and 218 are providedover the conductive films 210, 211, 212, 213, 214, and 215. Theinsulating film 218 is preferably an insulator having planarity. Theinsulating films 216, 217, and 218 have openings 219 and 220. Aconductive film 221 is provided over the insulating film 218. Theconductive film 221 is electrically connected to the conductive film 204through the opening 220. At least part of the conductive film 221functions as a common electrode. An insulating film 222 is provided overthe conductive film 221. An opening 223 is provided into the insulatingfilm 222. A conductive film 224 is provided over the insulating film222. The conductive film 224 is electrically connected to the conductivefilm 211 through the opening 223. At least part of the conductive film224 can function as a pixel electrode. The conductive film 224 includesat least one slit, whereby the liquid crystal can be controlled by anelectric field generated between the conductive films 224 and 221. Atleast part of the conductive film 221 overlaps with at least part of theconductive film 224 with the insulating film 222 interposed therebetweenand functions as an electrode forming a storage capacitor for storing apotential of the pixel electrode for a predetermined period. A liquidcrystal layer 226 is provided over the conductive film 224. A coloringfilm 227 and a light-blocking film 228 are provided over the liquidcrystal layer 226. As the color filter 227, a red (R) color filter, agreen (G) color filter, and a blue (B) color filter can be used. Thesecolors may also be combined with a white (W) or yellow (Y) color filter.A substrate 229 is provided over the coloring film 227 and thelight-blocking film 228. A conductive film 225 is provided under thesubstrate 201. The conductive film 225 overlaps with the conductive film221 at least with the substrate 201 interposed therebetween andfunctions as the first capacitor of the sensor unit 101. A transparentconductive material is preferably used as the conductive films 221, 224,and 225.

At least part of the conductive film 221 overlaps with at least part ofthe conductive film 225 with a dielectric interposed therebetween,thereby forming a capacitor. In the active matrix touch sensor of oneembodiment of the present invention, capacitance formed between anobject to be detected such as a finger or a stylus and the conductivefilm 221 is measured to detect touch motion. Specifically, touch motioncan be detected by measuring a change in the potential of the conductivefilm 221 due to capacitance formed between the object to be detected andthe conductive film 221 by the touch motion when a predeterminedpotential difference is applied between the conductive film 221 and theconductive film 225.

At least part of the conductive film 221 also functions as an electrodeof a storage capacitor for storing a voltage of the pixel electrode fora predetermined period and further functions as an electrode of a firstcapacitor provided in the sensor unit 101 for detecting touch motion.

The liquid crystal display device integrated with the active matrixtouch sensor of one embodiment of the present invention can detectpositional information based on the change in capacitance at the time oftouch motion. Images can be displayed on the display region. Because theactive matrix touch sensor, the gate line 104, the source line 105, thetransistor 106, and the pixel electrode 107 are formed over thesubstrate 201, a thin and light liquid crystal display device integratedwith the active matrix touch sensor can be obtained. A transistor usedfor the active matrix touch sensor can be formed at the same time as thetransistor 106 in the pixel, which can simplify the fabricating processand reduce the fabricating cost.

A structure of a transistor used for the liquid crystal display deviceintegrated with the active matrix touch sensor of one embodiment of thepresent invention is not particularly limited and transistors withvarious structures can be used. Although the bottom-gate transistor isshown in this embodiment, the transistor is not limited to this. Forexample, a top-gate transistor may be used.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 2

FIG. 3 is a cross-sectional view of a liquid crystal display deviceintegrated with an active matrix touch sensor of one embodiment of thepresent invention. In FIG. 3 , a cross section a-a′ illustrates part ofa display element; b-b′, a sensor unit; and c-c′, part of circuit.

FIG. 2 illustrates a structure in which the conductive film 225 isprovided under the substrate 201. FIG. 3 illustrates an example in whicha conductive film 301 corresponding to the conductive film 225 isprovided on the substrate 229 side. Since the structure provided overthe substrate 201 in FIG. 3 is similar to that of FIG. 2 except for theconductive film 225, the description is omitted. An example in which aconductive film 301 is provided over the liquid crystal is described inFIG. 3 .

In one embodiment of the present invention, the conductive film 301overlaps with the conductive film 224 with the liquid crystal layer 226interposed therebetween. In the structure of FIG. 3 , the liquid crystalis controlled by the conductive films 221, 224, and 301. The specificresistivity of the liquid crystal material used for the liquid crystalis preferably greater than or equal to 1.0×10¹³ Ω·cm, further preferablygreater than or equal to 1.0×10¹⁵ Ω·cm. A negative liquid crystalmaterial is preferably used for the liquid crystal. With this structure,the liquid crystal display device causes less change in transmittance ofthe liquid crystal and few image flickers perceivable by users even whenthe number of operations for writing image signals in a given period isreduced. Specifically, the liquid crystal molecules are controlled by anelectric field generated between the conductive films 224 and 221, andthe use of the conductive film 301 makes it possible for the alignmentof the liquid crystal to be controlled more stably. A potential of theconductive film 301 is preferably equal to that of the conductive film221. A transparent conductive material is preferably used as theconductive film 301.

A structure of a transistor used for the liquid crystal display deviceintegrated with the active matrix touch sensor of one embodiment of thepresent invention is not particularly limited and transistors withvarious structures can be used. Although bottom-gate transistors areshown in this embodiment, this embodiment is not limited to this. Forexample, top-gate transistors may be used.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 3

In this embodiment, a driving method by which the frequency of screenupdating is reduced as much as possible is described as a method fordriving a liquid crystal of one embodiment of the present invention.

A liquid crystal display device to which the driving method is applieddisplays images by at least two driving methods (modes). One is adriving method in which screen updating is successively performed. Thismethod is called “normal driving.” The other is a driving method inwhich screen writing is stopped after screen writing processing isexecuted. This method is called “idling stop (IDS) driving. In a “normalmode (state)” and an “IDS mode (state),” the liquid crystal displaydevice is operated by the normal drive and the IDS drive, respectively.

Moving images are displayed by the normal drive. Still images aredisplayed by the normal drive or the IDS drive. For displaying stillimages, the same picture is displayed; therefore, screen updating is notnecessarily performed successively. The liquid crystal display device isoperated by the IDS driving for displaying still images, which canreduce flicker in the images. The power consumption can also be reduced.The normal driving and the IDS driving are described below withreference to FIGS. 4A and 4B and FIGS. 5A and 5B.

FIG. 4A shows a display method of still images by the normal drive, andFIG. 4B shows a display method of still images by the IDS drive.

FIGS. 5A and 5B are timing chart examples of the normal driving and theIDS driving, respectively. In FIGS. 5A and 5B, Video is an image signalinput to the liquid crystal display device, which is an image datasignal supplied to a source line from a source line driver circuit. GVDDis a power supply voltage on a high potential side of the gate linedriver circuit.

In the normal drive, screen (data) is updated successively.Specifically, when the frame frequency is 60 Hz, one frame period isabout 1/60 seconds; thus, screen is updated every about 1/60 second.

In the IDS driving, processing performed as shown in the timing chartincludes data updating processing (also referred to as writingprocessing) and data retention processing.

Regarding the frequency of data updating, data updating is executed onceper frame period (period Tpd) as in the normal drive, whereby data iswritten to a pixel. After data is written, data updating is stopped. Apixel transistor is turned off so that data is retained.

The number of data updating operations in one data updating processingmay be one or more. FIG. 4B and FIG. 5B each show an example in whichthe number of data updating operations is three.

The number of data updating operations can be set in consideration ofthe length of the one frame period. The time required for data updatingoperation is at most 1 second, and is preferably about less than orequal to 0.5 seconds, or about less than or equal to 0.2 seconds.

The number of data writing operations is preferably adjusted so that thepolarity of Video signal retained in the pixel in the data retentionperiod is opposite to that of Video signal retained in the pixel in thepreceding data retention period. This can inhibit degradation of theliquid crystal due to the IDS driving.

As can be seen from FIGS. 4A and 4B and FIGS. 5A and 5B, in the IDSmode, a still image can be displayed while data is updated much lessfrequently than in the normal mode. Accordingly, display of still imagesin the IDS mode results in reduced screen flicker and less eye strain.In the data retention period, the gate line driver circuit and thesource line driver circuit also stop operating; thus, power consumptioncan be reduced.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 4

In this embodiment, a structure example of a touch sensor of oneembodiment of the present invention and a driving method thereof isdescribed with reference to drawings.

FIG. 6 illustrates a circuit diagram of a display portion including anactive matrix touch sensor of one embodiment of the present invention.FIG. 7 shows an example of signals which can be input to the circuit ofFIG. 6 .

The display portion in FIG. 6 includes at least a sensor unit and apixel. The sensor unit includes at least a capacitor C1, and transistorsM1, M2, and M3. The pixel includes at least a liquid crystal element LC,a capacitor Clc, and a transistor Mp.

A gate line Gpixel (l) is electrically connected to a gate of thetransistor Mp. A source line Spixel (o) is electrically connected to oneof a source and a drain of the transistor Mp (l and o are each aninteger of 1 or more). The other of the source and the drain of thetransistor Mp is electrically connected to a pixel electrode and a firstelectrode of the capacitor Clc.

A scanning line GL (k) is electrically connected to a gate of thetransistor M2. A wiring DL (n) is electrically connected to one of asource and a drain of the transistor M2 (k and n are each an integer of1 or more). A wiring VRES is electrically connected to one of a sourceand a drain of the transistor M3. A wiring RES is electrically connectedto a gate of the transistor M3. A wiring VPI is electrically connectedto one of a source and a drain of the transistor M1. A wiring CS iselectrically connected to the second electrode of the capacitor C1.

The other of the source and the drain of the transistor M1 and the otherof the source and the drain of the transistor M2 are electricallyconnected to each other. A gate of the transistor M1 is electricallyconnected to the other of the source and the drain of the transistor M3and the first electrode of the capacitor C1.

A common electrode COM included in the liquid crystal element LC iselectrically connected to the gate of the transistor M1. The secondelectrode of the capacitor Clc in the pixel portion is electricallyconnected to the gate of the transistor M1.

The gate line Gpixel is electrically connected to the gate line drivercircuit. The source line Spixel is electrically connected to the sourceline driver circuit. The wiring VRES is electrically connected to asensor unit driver circuit. The wiring RES is electrically connected tothe sensor unit driver circuit. The wiring CS and the wiring VPI eachmay be electrically connected to the sensor unit driver circuit orelectrically connected to a FPC otherwise than via the sensor unitdriver circuit.

The wiring DL is electrically connected to a conversion circuit. Any ofa variety of circuits can be used as the conversion circuit. FIG. 8illustrates one example.

The sensor unit includes the capacitor C1 including the first electrodeand the second electrode. In FIG. 2 , the conductive film 225corresponds to the second electrode and the conductive film 221corresponds to the first electrode. In FIG. 3 , the conductive film 301corresponds to the second electrode and the conductive film 221corresponds to the first electrode.

A driving method is described with reference to FIG. 6 and FIG. 7 .

A timing chart of one frame period is shown in FIG. 7 . One frame periodincludes a writing period and a sensing period. The writing period is aperiod in which image signals are written to each of the pixels of thedisplay portion. The sensing period is a period in which touch motion isdetected from the sensor unit.

[Writing Period]

[First Step]

When a control signal is input to the wiring RES, so that the wiring RESis selected, the transistor M3, which is electrically connected to thewiring RES, is turned on. A low potential is supplied to the wiringVRES. The potential supplied to the wiring VRES is supplied to thecommon electrode COM through the transistor M3 in the on state. In sucha manner, the common electrode in the pixel has an electrical connectionto the wiring VRES and has a constant potential during the updatingperiod.

[Second Step]

The gate line Gpixel is selected. The transistor Mp, which is connectedto the selected gate line Gpixel, is turned on. A video signal suppliedto the source line Spixel is supplied to the pixel electrode and thecapacitor Clc through the transistor Mp. In such a manner, the gatelines Gpixel in the first to the last rows are sequentially selected,and video signals are written to each of the pixel electrodes and eachof the capacitors Clc. In FIG. 7 , a timing chart from Gpixel (l) toGpixel (l+m) (m is an integer of 1 or more) is shown as an example.

[Sensing Period]

[Third Step]

In the sensing period, none of the gate lines Gpixel is selected and thetransistor Mp is turned off.

[Fourth Step]

The potentials of the wirings VPI and CS are low. The wiring RES isselected and the transistor M3 is turned on. A high potential issupplied to the wiring VRES and a high potential is supplied to the gateof the transistor M1. At this time, a low potential is supplied to thesecond electrode of the capacitor C1 electrically connected to thewiring CS, and a high potential is supplied to the first electrode ofthe capacitor C1 electrically connected to the gate of the transistorM1. For example, when the low potential is 0V and the high potential is5V, a voltage of 5V is applied between the second potential and thefirst potential of the capacitor C1. Then, the wiring RES is notselected so that the transistor M3 is turned off, and voltages at bothends of the capacitor C1 are retained.

[Fifth Step]

In the case where the capacitor C1 is put in the air, when an objectwhose dielectric constant is higher than that of the air, for example ahuman finger 901, is placed in the proximity to the first electrode ofthe capacitor C1, the capacitance C2 is generated between the firstelectrode of the capacitor C1 and the finger (see FIG. 9 ). In thisstate, the potential of the wiring CS is shifted from low to high. Agate potential of part of the transistor M1 where an object whosedielectric constant is higher than that of the air, for example a humanfinger, is placed in the proximity to the first electrode of thecapacitor C1 is less likely to be changed compared to a gate potentialof part of the transistor M1 where an object whose dielectric constantis higher than that of the air, for example a human finger, is notplaced in the proximity to the first electrode of the capacitor C1.Measuring this difference determines the position of a human finger, forexample. For measuring this difference, the conversion circuit in FIG. 8can be used, for example.

In the conversion circuit 50 of FIG. 8 , the transistor M4 in theconversion circuit is turned on by a signal supplied from the wiringsVPO and BR while the transistor M2 in the sensor unit is turned off, sothat the potential of the wiring DL is set to a determined potential.After that, the transistor M4 is turned off. Then, the transistor M2 inthe sensor unit is turned on, and the change in the potential of thewiring DL is measured. After the measurement for one screen is executed,the potential of the wiring CS is shifted to low.

As described above, the operation in one frame includes the first tofifth steps.

The IDS driving in Embodiment 3 can be used in combination.

This embodiment shows an example of the touch sensor of one embodimentof the present invention. Note that one embodiment of the presentinvention is not limited to the above examples. For example, the touchsensor of one embodiment of the present invention can be of resistive,surface acoustic wave, infrared, electromagnetic induction, surfacecapacitive, or projected capacitive type.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 5

FIG. 10 is a cross-sectional view of a liquid crystal display deviceintegrated with an active matrix touch sensor of one embodiment of thepresent invention. In FIG. 10 , a cross section a-a′ illustrates part ofa display element; b-b′, a sensor unit; and c-c′, part of circuit.

FIG. 2 illustrates a structure in which the conductive film 225 isprovided under the substrate 201. FIG. 10 illustrates an example inwhich the conductive film 225 is not provided. In the circuit diagram inFIG. 6 , the conductive film 225 corresponds to the wiring CS. FIG. 11illustrates a circuit diagram of a display portion in which a layercorresponding to the conductive film 225 in FIG. 2 is not provided asillustrated in FIG. 10 . The sensor unit includes the capacitor C1including the first electrode and the second electrode. In FIG. 10 , theconductive film 221 corresponds to the first electrode, and theconductive film 221 that is not connected to the transistor in thesensor unit corresponds to the second electrode. Since the stackedstructure of FIG. 10 is similar to that of FIG. 2 except for theconductive film 225, the description is omitted.

In FIG. 11 , the common electrode of part of the pixel functions as thewiring CS. That is, although the conductive film 225 is provided in FIG.2 to be used as the wiring CS, part of the conductive film 221functioning as the common electrode is patterned and used as the wiringCS in FIG. 11 ; therefore, the conductive film 225 is not necessarilyprovided as the wiring CS. FIG. 12 illustrates an example of a layout ofthe conductive film 221. In the example in FIG. 12 , an electrode 1201corresponds to the second electrode of the capacitor C1, and anelectrode 1202 corresponds to the first electrode of the capacitor C1.

FIG. 11 illustrates a circuit diagram of a display portion including anactive matrix touch sensor of one embodiment of the present invention.FIG. 7 is a timing chart of one example of signals which can be input tothe circuit in FIG. 11 .

The IDS driving in Embodiment 3 can be used in combination.

This embodiment shows an example of the touch sensor of one embodimentof the present invention. Note that one embodiment of the presentinvention is not limited to the above examples. For example, the touchsensor of one embodiment of the present invention can be of resistive,surface acoustic wave, infrared, electromagnetic induction, surfacecapacitive, or projected capacitive type.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 6

An insulator, a semiconductor, and a conductor that can be favorablyused for a semiconductor device of one embodiment of the presentinvention, and a formation method and a processing method thereof aredescribed in this embodiment.

The insulator can be formed with a single layer or a stack using siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminumnitride, and the like.

As a high-dielectric constant material (also referred to as a high-kmaterial) that can be used as the insulator, a metal oxide such as atantalum oxide, a hafnium oxide, a hafnium silicate oxide, a zirconiumoxide, an aluminum oxide, or a titanium oxide; or a rare-earth oxidesuch as a lanthanum oxide, can be used.

In the case of using an oxide semiconductor for the semiconductor, anoxide material from which oxygen is partly released due to heating ispreferably used for the insulator which is in contact with the oxidesemiconductor. As the oxide material from which oxygen is released dueto heating, oxide containing oxygen in excess of the stoichiometriccomposition is preferably used, for example. The oxide film containingoxygen in excess of the stoichiometric composition is an oxide film ofwhich the amount of released oxygen converted into oxygen atoms isgreater than or equal to 1.0×10¹⁸ atoms/cm³, and preferably greater thanor equal to 3.0×10²⁰ atoms/cm³ in thermal desorption spectroscopy (TDS)analysis at a surface temperature of the film of higher than or equal to100° C. and lower than or equal to 700° C., or higher than or equal to100° C. and lower than or equal to 500° C. For example, as such amaterial, a material containing silicon oxide or silicon oxynitride ispreferably used. Alternatively, a metal oxide can be used. In thisspecification, “silicon oxynitride” refers to a material that containsoxygen at a higher proportion than nitrogen, and “silicon nitride oxide”refers to a material that contains nitrogen at a higher proportion thanoxygen.

The insulator may be formed by a sputtering method, a chemical vapordeposition (CVD) method (including a thermal CVD method, a metal organicCVD (MOCVD) method, a plasma enhanced CVD (PECVD) method, and the like),a molecular beam epitaxy (MBE) method, an atomic layer deposition (ALD)method, a pulsed laser deposition (PLD) method, or the like.

For the insulator having planarity, a heat-resistant organic material,such as polyimide, acrylic, benzocyclobutene-based resin, polyamide, orepoxy can be used. Other than such organic materials, it is alsopossible to use a siloxane-based resin, PSG (phosphosilicate glass),BPSG (borophosphosilicate glass), or the like. Note that the insulatormay be formed by stacking a plurality of insulating films formed usingthese materials. Depending on the material, the insulator can be formedby a method such as a CVD method, a sputtering method, an SOG method,spin coating, dipping, spray coating, or a droplet discharge method(such as an ink-jet method), a printing method (such as screen printingor offset printing), or with a tool (equipment) such as a doctor knife,a roll coater, a curtain coater, or a knife coater.

As a method for forming the insulator having planarity, other than theabove-described method, a chemical mechanical polishing (CMP) method canbe used. After the formation of the insulator, the surface of theinsulator is subjected to CMP treatment, so that a plane surface can beobtained.

For the semiconductor, a semiconductor such as a polycrystallinesemiconductor, a microcrystalline semiconductor, an amorphoussemiconductor, or a compound semiconductor can be used. For example,amorphous silicon, polycrystalline silicon or single crystal silicon, orsuch a semiconductor doped with an element belonging to Group 15 such asphosphorus of the periodic table may be used. Alternatively, an oxidesemiconductor such as an In—Ga—Zn—O-based oxide semiconductor may beused.

A metal formed with aluminum, titanium, chromium, nickel, copper,yttrium, zirconium, molybdenum, silver, tantalum, niobium, or tungsten,or an alloy material or a compound material containing any of these asits main component can be used for the conductor. Alternatively,polycrystalline silicon to which an impurity such as phosphorus is addedcan be used. The conductor may have a single-layer structure or a stackof a plurality of materials. For example, a single-layer structure of analuminum film containing silicon, a two-layer structure in which analuminum film is stacked over a titanium film, a two-layer structure inwhich an aluminum film is stacked over a tungsten film, a two-layerstructure in which a copper film is stacked over acopper-magnesium-aluminum alloy film, a two-layer structure in which acopper film is stacked over a titanium film, a two-layer structure inwhich a copper film is stacked over a tungsten film, a three-layerstructure in which a titanium film or a titanium nitride film, analuminum film or a copper film, and a titanium film or a titaniumnitride film are stacked in this order, a three-layer structure in whicha molybdenum film or a molybdenum nitride film, an aluminum film or acopper film, and a molybdenum film or a molybdenum nitride film arestacked in this order, and the like can be given. When the metal nitridefilm is provided, adhesiveness of the metal film can be increased; thus,separation can be prevented. Note that a transparent conductive materialcontaining indium oxide, tin oxide, or zinc oxide may be used.

The conductor can be formed by a sputtering method, an evaporationmethod, a CVD method, or the like. The CVD method can be classified intoa plasma enhanced CVD (PECVD) method using plasma, a thermal CVD (TCVD)method using heat, and the like. Depending on the used source gas, theCVD method can be classified into a metal CVD (MCVD) method and a metalorganic CVD (MOCVD) method. By using the PECVD method, a high-qualityfilm can be formed at a relatively low temperature. By using the TCVDmethod, in which plasma is not used, a film can be formed with fewdefects because damage caused by plasma does not occur.

Here, a method for processing a film is described. In the case of finelyprocessing a film, a variety of fine processing techniques can be used.For example, a method may be used in which a resist mask formed by aphotolithography process or the like is subjected to thinning treatment.Alternatively, a method may be used in which a dummy pattern is formedby a photolithography process or the like, the dummy pattern is providedwith a sidewall and is then removed, and a film is etched using theremaining sidewall as a resist mask. In order to achieve a high aspectratio, anisotropic dry etching is preferably used for etching of a film.Alternatively, a hard mask formed of an inorganic film or a metal filmmay be used.

As light used to form the resist mask, light with an i-line (with awavelength of 356 nm), light with a g-line (with a wavelength of 436nm), light with an h-line (with a wavelength of 405 nm), or light inwhich the i-line, the g-line, and the h-line are mixed can be used.Alternatively, KrF laser light, ArF laser light, or the like can beused. Exposure may be performed by liquid immersion exposure technique.As the light for the exposure, extreme ultra-violet light (EUV) orX-rays may be used. Instead of the light for the exposure, an electronbeam can be used. It is preferable to use extreme ultra-violet light,X-rays, or an electron beam because extremely minute processing can beperformed. Note that in the case of performing exposure by scanning abeam such as an electron beam, a photomask is not needed.

An organic resin film having a function of improving adhesion betweenthe film to be processed and a resist film may be formed before theresist film serving as a resist mask is formed. The organic resin filmcan be formed to have a plane surface by covering a step thereunder by aspin coating method or the like, and thus can reduce variation inthickness of the resist mask over the organic resin film. In the case offine processing, in particular, a material serving as a film having afunction of preventing reflection of light for the exposure ispreferably used for the organic resin film. Examples of such an organicresin film include a bottom anti-reflection coating (BARC) film. Theorganic resin film may be removed at the same time as the removal of theresist mask or after the removal of the resist mask.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 7

An oxide semiconductor that can be favorably used for a semiconductorfilm of one embodiment of the present invention is described in thisembodiment.

An oxide semiconductor has a wide energy gap of 3.0 eV or more. Atransistor including an oxide semiconductor film obtained by processingof the oxide semiconductor in an appropriate condition and a sufficientreduction in carrier density of the oxide semiconductor can have muchlower leakage current between a source and a drain in an off state(off-state current) than a conventional transistor including silicon.

An applicable oxide semiconductor preferably contains at least indium(In) or zinc (Zn). In particular, In and Zn are preferably contained. Inaddition, as a stabilizer for reducing variation in electriccharacteristics of the transistor using the oxide semiconductor, one ormore selected from gallium (Ga), tin (Sn), hafnium (Hf), zirconium (Zr),titanium (Ti), scandium (Sc), yttrium (Y), and an lanthanoid (such ascerium (Ce), neodymium (Nd), or gadolinium (Gd), for example) ispreferably contained.

As the oxide semiconductor, for example, any of the following can beused: indium oxide, tin oxide, zinc oxide, an In—Zn-based oxide, aSn—Zn-based oxide, an Al—Zn-based oxide, a Zn—Mg-based oxide, aSn—Mg-based oxide, an In—Mg-based oxide, an In—Ga-based oxide, anIn—Ga—Zn-based oxide (also referred to as IGZO), an In—Al—Zn-basedoxide, an In—Sn—Zn-based oxide, a Sn—Ga—Zn-based oxide, anAl—Ga—Zn-based oxide, a Sn—Al—Zn-based oxide, an In—Hf—Zn-based oxide,an In—Zr—Zn-based oxide, an In—Ti—Zn-based oxide, an In—Sc—Zn-basedoxide, an In—Y—Zn-based oxide, an In—La—Zn-based oxide, anIn—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide,an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-basedoxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, anIn—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide,an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or anIn—Hf—Al—Zn-based oxide.

Here, an “In—Ga—Zn-based oxide” means an oxide containing In, Ga, and Znas its main components and there is no particular limitation on theratio of In, Ga, and Zn. The In—Ga—Zn-based oxide may contain anothermetal element in addition to In, Ga, and Zn.

Alternatively, a material represented by In_(1+α)M_(1−α)O₃(ZnO)_(m)(−1≤α≤1, m>0, and m is not an integer) may be used as an oxidesemiconductor. Note that M represents one or more metal elementsselected from Ga, Fe, Mn, and Co, or the above-described element as astabilizer. Alternatively, as the oxide semiconductor, a materialrepresented by In₂SnO₅(ZnO)_(n) (n>0, and n is a natural number) may beused.

For example, In—Ga—Zn-based oxide with an atomic ratio ofIn:Ga:Zn=1:1:1, 1:3:2, 1:3:4, 1:3:6, 3:1:2, or 2:1:3, or an oxide whosecomposition is in the neighborhood of the above compositions may beused.

When an oxide semiconductor film contains a large amount of hydrogen,the hydrogen and an oxide semiconductor are bonded to each other, sothat part of the hydrogen serves as a donor and causes generation of anelectron which is a carrier. As a result, the threshold voltage of thetransistor shifts in the negative direction. Therefore, it is preferablethat, after formation of the oxide semiconductor film, dehydrationtreatment (dehydrogenation treatment) be performed to remove hydrogen ormoisture from the oxide semiconductor film so that the oxidesemiconductor film is highly purified to contain impurities as little aspossible.

Note that oxygen in the oxide semiconductor film is also reduced by thedehydration treatment (dehydrogenation treatment) in some cases. Forthis reason, it is preferred that oxygen be added to the oxidesemiconductor to fill oxygen vacancies increased by the dehydrationtreatment (dehydrogenation treatment). In this specification and thelike, supplying oxygen to an oxide semiconductor film may be expressedas oxygen adding treatment, and treatment for making the oxygen contentof an oxide semiconductor film be in excess of that in thestoichiometric composition may be expressed as treatment for making anoxygen-excess state.

In this manner, hydrogen or moisture is removed from the oxidesemiconductor film by the dehydration treatment (dehydrogenationtreatment) and oxygen vacancies therein are filled by the oxygen addingtreatment, whereby the oxide semiconductor film can be turned into ani-type (intrinsic) oxide semiconductor film or a substantially i-type(intrinsic) oxide semiconductor film which is extremely close to ani-type oxide semiconductor film. Note that “substantially intrinsic”means that the oxide semiconductor film contains extremely few (close tozero) carriers derived from a donor and has a carrier density which is1×10¹⁷/cm³ or lower, 1×10¹⁶/cm³ or lower, 1×10¹⁵/cm³ or lower,1×10¹⁴/cm³ or lower, or 1×10¹³/cm³ or lower.

Thus, the transistor including an i-type or substantially i-type oxidesemiconductor film can have extremely favorable off-state currentcharacteristics. For example, the drain current at the time when thetransistor including an oxide semiconductor film is in an off-state canbe less than or equal to 1×10⁻¹⁸ A, preferably less than or equal to1×10⁻²¹ A, further preferably less than or equal to 1×10⁻²⁴ A at roomtemperature (about 25° C.); or less than or equal to 1×10⁻¹⁵ A,preferably less than or equal to 1×10⁻¹⁸ A, further preferably less thanor equal to 1×10⁻²¹ A at 85° C. Note that an off state of an n-channeltransistor refers to a state where the gate voltage is sufficientlylower than the threshold voltage. Specifically, the transistor is in anoff state when the gate voltage is lower than the threshold voltage by1V or more, preferably by 2V or more, or 3V or more.

<Structure of Oxide Semiconductor>

A structure of an oxide semiconductor is described below.

An oxide semiconductor is classified into a single crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofa non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a nanocrystalline oxide semiconductor (nc-OS), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

From another perspective, an oxide semiconductor is classified into anamorphous oxide semiconductor and a crystalline oxide semiconductor.Examples of a crystalline oxide semiconductor include a single crystaloxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor,and an nc-OS.

It is known that an amorphous structure is generally defined as beingmetastable and unfixed, and being isotropic and having no non-uniformstructure. In other words, an amorphous structure has a flexible bondangle and a short-range order but does not have a long-range order.

This means that an inherently stable oxide semiconductor cannot beregarded as a completely amorphous oxide semiconductor. Moreover, anoxide semiconductor that is not isotropic (e.g., an oxide semiconductorthat has a periodic structure in a microscopic region) cannot beregarded as a completely amorphous oxide semiconductor. Note that ana-like OS has a periodic structure in a microscopic region, but at thesame time has a void and has an unstable structure. For this reason, ana-like OS has physical properties similar to those of an amorphous oxidesemiconductor.

<CAAC-OS>

First, a CAAC-OS is described.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.In addition, the term “substantially parallel” indicates that the angleformed between two straight lines is greater than or equal to −30° andless than or equal to 30°. The term “perpendicular” indicates that theangle formed between two straight lines is greater than or equal to 80°and less than or equal to 100°, and accordingly also includes the casewhere the angle is greater than or equal to 85° and less than or equalto 95°. The term “substantially perpendicular” indicates that the angleformed between two straight lines is greater than or equal to 60° andless than or equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

The CAAC-OS is one of oxide semiconductors having a plurality of c-axisaligned crystal parts (also referred to as pellets).

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OS,which is obtained using a transmission electron microscope (TEM), aplurality of pellets can be observed. However, in the high-resolutionTEM image, a boundary between pellets, that is, a grain boundary is notclearly observed. Thus, in the CAAC-OS, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

A CAAC-OS observed with TEM will be described below. FIG. 13A shows ahigh-resolution TEM image of a cross section of the CAAC-OS which isobserved from a direction substantially parallel to the sample surface.The high-resolution TEM image is obtained with a spherical aberrationcorrector function. The high-resolution TEM image obtained with aspherical aberration corrector function is particularly referred to as aCs-corrected high-resolution TEM image. The Cs-corrected high-resolutionTEM image can be obtained with, for example, an atomic resolutionanalytical electron microscope JEM-ARM200F manufactured by JEOL Ltd.

FIG. 13B is an enlarged Cs-corrected high-resolution TEM image of aregion (1) in FIG. 13A. FIG. 13B shows that metal atoms are arranged ina layered manner in a pellet. Each metal atom layer has a configurationreflecting unevenness of a surface over which a CAAC-OS film is formed(hereinafter, the surface is referred to as a formation surface) or atop surface of the CAAC-OS film, and is arranged parallel to theformation surface or the top surface of the CAAC-OS film.

As shown in FIG. 13B, the CAAC-OS has a characteristic atomicarrangement. The characteristic atomic arrangement is denoted by anauxiliary line in FIG. 13C. FIGS. 13B and 13C prove that the size of apellet is approximately greater than or equal to 1 nm and less than orequal to 3 nm, and the size of a space caused by tilt of the pellets isapproximately 0.8 nm. Therefore, the pellet can also be referred to as ananocrystal (nc). Furthermore, the CAAC-OS can also be referred to as anoxide semiconductor including c-axis aligned nanocrystals (CANC).

Here, according to the Cs-corrected high-resolution TEM images, theschematic arrangement of pellets 5100 of a CAAC-OS over a substrate 5120is illustrated by such a structure in which bricks or blocks are stacked(see FIG. 13D). The part in which the pellets are tilted as observed inFIG. 13C corresponds to a region 5161 shown in FIG. 13D.

FIG. 14A shows a Cs-corrected high-resolution TEM image of a plane ofthe CAAC-OS observed from a direction substantially perpendicular to thesample surface. FIGS. 14B, 14C, and 14D are enlarged Cs-correctedhigh-resolution TEM images of regions (1), (2), and (3) in FIG. 14A,respectively. FIGS. 14B, 14C, and 14D indicate that metal atoms arearranged in a triangular, quadrangular, or hexagonal configuration in apellet. However, there is no regularity of arrangement of metal atomsbetween different pellets.

Next, a CAAC-OS analyzed by X-ray diffraction (XRD) will be described.For example, when the structure of a CAAC-OS including an InGaZnO₄crystal is analyzed by an out-of-plane method, a peak appears at adiffraction angle (2θ) of around 31° as shown in FIG. 15A. This peak isderived from the (009) plane of the InGaZnO₄ crystal, which indicatesthat crystals in the CAAC-OS have c-axis alignment, and that the c-axesare aligned in a direction substantially perpendicular to the formationsurface or the top surface of the CAAC-OS.

Note that in structural analysis of the CAAC-OS by an out-of-planemethod, another peak may appear when 2θ is around 36°, in addition tothe peak at 2θ of around 31°. The peak at 2θ of around 36° indicatesthat a crystal having no c-axis alignment is included in part of theCAAC-OS. It is preferable that, in the CAAC-OS analyzed by anout-of-plane method, a peak appear when 2θ is around 31° and that a peaknot appear when 2θ is around 36°.

On the other hand, in structural analysis of the CAAC-OS by an in-planemethod in which an X-ray beam is incident on a sample in a directionsubstantially perpendicular to the c-axis, a peak appears when 2θ isaround 56°. This peak is attributed to the (110) plane of the InGaZnO₄crystal. In the case of the CAAC-OS, when analysis (ϕ scan) is performedwith 2θ fixed at around 56° and with the sample rotated using a normalvector of the sample surface as an axis (ϕ axis), as shown in FIG. 15B,a peak is not clearly observed. In contrast, in the case of a singlecrystal oxide semiconductor of InGaZnO₄, when ϕ scan is performed with2θ fixed at around 56°, as shown in FIG. 15C, six peaks which arederived from crystal planes equivalent to the (110) plane are observed.Accordingly, the structural analysis using XRD shows that the directionsof a-axes and b-axes are irregularly oriented in the CAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction will be described. Forexample, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in a directionparallel to the sample surface, a diffraction pattern (also referred toas a selected-area transmission electron diffraction pattern) shown inFIG. 16A can be obtained. In this diffraction pattern, spots derivedfrom the (009) plane of an InGaZnO₄ crystal are included. Thus, theelectron diffraction also indicates that pellets included in the CAAC-OShave c-axis alignment and that the c-axes are aligned in a directionsubstantially perpendicular to the formation surface or the top surfaceof the CAAC-OS. Meanwhile, FIG. 16B shows a diffraction pattern obtainedin such a manner that an electron beam with a probe diameter of 300 nmis incident on the same sample in a direction perpendicular to thesample surface. As shown in FIG. 16B, a ring-like diffraction pattern isobserved. Thus, the electron diffraction also indicates that the a-axesand b-axes of the pellets included in the CAAC-OS do not have regularalignment. The first ring in FIG. 16B is considered to be derived fromthe (010) plane, the (100) plane, and the like of the InGaZnO₄ crystal.The second ring in FIG. 16B is considered to be derived from the (110)plane and the like.

As described above, the CAAC-OS is an oxide semiconductor with highcrystallinity. Entry of impurities, formation of defects, or the likemight decrease the crystallinity of an oxide semiconductor. This meansthat the CAAC-OS has small amounts of impurities and defects (e.g.,oxygen vacancies).

Note that the impurity means an element other than the main componentsof the oxide semiconductor, such as hydrogen, carbon, silicon, or atransition metal element. For example, an element (specifically, siliconor the like) having higher strength of bonding to oxygen than a metalelement included in an oxide semiconductor extracts oxygen from theoxide semiconductor, which results in disorder of the atomic arrangementand reduced crystallinity of the oxide semiconductor. A heavy metal suchas iron or nickel, argon, carbon dioxide, or the like has a large atomicradius (or molecular radius), and thus disturbs the atomic arrangementof the oxide semiconductor and decreases crystallinity.

The characteristics of an oxide semiconductor having impurities ordefects might be changed by light, heat, or the like. For example,impurities contained in the oxide semiconductor might serve as carriertraps or carrier generation sources. Furthermore, oxygen vacancies inthe oxide semiconductor serve as carrier traps or serve as carriergeneration sources when hydrogen is captured therein.

The CAAC-OS having small amounts of impurities and oxygen vacancies isan oxide semiconductor with a low carrier density (specifically, lowerthan 8×10¹¹/cm³, preferably lower than 1×10¹¹/cm³, further preferablylower than 1×10¹⁰/cm³, and is higher than or equal to 1×10⁻⁹/cm³). Suchan oxide semiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.Thus, the CAAC-OS can be referred to as an oxide semiconductor havingstable characteristics.

<nc-OS>

Next, an nc-OS will be described.

An nc-OS has a region in which a crystal part is observed and a regionin which a crystal part is not clearly observed in a high-resolution TEMimage. In most cases, the size of a crystal part included in the nc-OSis greater than or equal to 1 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 3 nm. Note thatan oxide semiconductor including a crystal part whose size is greaterthan 10 nm and less than or equal to 100 nm is sometimes referred to asa microcrystalline oxide semiconductor. In a high-resolution TEM imageof the nc-OS, for example, a grain boundary is not clearly observed insome cases. Note that there is a possibility that the origin of thenanocrystal is the same as that of a pellet in a CAAC-OS. Therefore, acrystal part of the nc-OS may be referred to as a pellet in thefollowing description.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different pellets in thenc-OS. Thus, the orientation of the whole film is not observed.Accordingly, the nc-OS cannot be distinguished from an a-like OS or anamorphous oxide semiconductor, depending on an analysis method. Forexample, when the nc-OS is analyzed by an out-of-plane method using anX-ray beam having a diameter larger than the size of a pellet, a peakwhich shows a crystal plane does not appear. Furthermore, a diffractionpattern like a halo pattern is observed when the nc-OS is subjected toelectron diffraction using an electron beam with a probe diameter (e.g.,50 nm or larger) that is larger than the size of a pellet. Meanwhile,spots appear in a nanobeam electron diffraction pattern of the nc-OSwhen an electron beam having a probe diameter close to or smaller thanthe size of a pellet is applied. Moreover, in a nanobeam electrondiffraction pattern of the nc-OS, bright regions in a circular (ring)pattern are shown in some cases. Also in a nanobeam electron diffractionpattern of the nc-OS, a plurality of spots are shown in a ring-likeregion in some cases.

Since there is no regularity of crystal orientation between the pellets(nanocrystals) as mentioned above, the nc-OS can also be referred to asan oxide semiconductor including random aligned nanocrystals (RANC) oran oxide semiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has high regularity as comparedwith an amorphous oxide semiconductor. Therefore, the nc-OS is likely tohave a lower density of defect states than an a-like OS and an amorphousoxide semiconductor. Note that there is no regularity of crystalorientation between different pellets in the nc-OS. Therefore, the nc-OShas a higher density of defect states than the CAAC-OS.

<a-Like OS>

An a-like OS has a structure intermediate between those of the nc-OS andthe amorphous oxide semiconductor.

In a high-resolution TEM image of the a-like OS, a void may be observed.Furthermore, in the high-resolution TEM image, there are a region wherea crystal part is clearly observed and a region where a crystal part isnot observed.

The a-like OS has an unstable structure because it contains a void. Toverify that an a-like OS has an unstable structure as compared with aCAAC-OS and an nc-OS, a change in structure caused by electronirradiation is described below.

An a-like OS (referred to as Sample A), an nc-OS (referred to as SampleB), and a CAAC-OS (referred to as Sample C) are prepared as samplessubjected to electron irradiation. Each of the samples is an In—Ga—Znoxide.

First, a high-resolution cross-sectional TEM image of each sample isobtained. The high-resolution cross-sectional TEM images show that allthe samples have crystal parts.

Note that which part is regarded as a crystal part is determined asfollows. It is known that a unit cell of an InGaZnO₄ crystal has astructure in which nine layers including three In—O layers and sixGa—Zn—O layers are stacked in the c-axis direction. The distance betweenthe adjacent layers is equivalent to the lattice spacing on the (009)plane (also referred to as d value). The value is calculated to be 0.29nm from crystal structural analysis. Accordingly, a portion where thelattice spacing between lattice fringes is greater than or equal to 0.28nm and less than or equal to 0.30 nm is regarded as a crystal part ofInGaZnO₄. Each of lattice fringes corresponds to the a-b plane of theInGaZnO₄ crystal.

FIG. 17 shows change in the average size of crystal parts (at 22 pointsto 45 points) in each sample. Note that the crystal part sizecorresponds to the length of a lattice fringe. FIG. 17 indicates thatthe crystal part size in the a-like OS increases with an increase in thecumulative electron dose. Specifically, as shown by (1) in FIG. 17 , acrystal part of approximately 1.2 nm (also referred to as an initialnucleus) at the start of TEM observation grows to a size ofapproximately 2.6 nm at a cumulative electron dose of 4.2×10⁸ e⁻/nm². Incontrast, the crystal part size in the nc-OS and the CAAC-OS showslittle change from the start of electron irradiation to a cumulativeelectron dose of 4.2×10⁸ e⁻/nm². Specifically, as shown by (2) and (3)in FIG. 17 , the average crystal sizes in an nc-OS and a CAAC-OS areapproximately 1.4 nm and approximately 2.1 nm, respectively, regardlessof the cumulative electron dose.

In this manner, growth of the crystal part in the a-like OS is inducedby electron irradiation. In contrast, in the nc-OS and the CAAC-OS,growth of the crystal part is hardly induced by electron irradiation.Therefore, the a-like OS has an unstable structure as compared with thenc-OS and the CAAC-OS.

The a-like OS has a lower density than the nc-OS and the CAAC-OS becauseit contains a void. Specifically, the density of the a-like OS is higherthan or equal to 78.6% and lower than 92.3% of the density of the singlecrystal oxide semiconductor having the same composition. The density ofeach of the nc-OS and the CAAC-OS is higher than or equal to 92.3% andlower than 100% of the density of the single crystal oxide semiconductorhaving the same composition. It is difficult to deposit an oxidesemiconductor having a density of lower than 78% of the density of thesingle crystal oxide semiconductor.

For example, in the case of an oxide semiconductor having an atomicratio of In:Ga:Zn=1:1:1, the density of single crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, thedensity of the a-like OS is higher than or equal to 5.0 g/cm³ and lowerthan 5.9 g/cm³. For example, in the case of the oxide semiconductorhaving an atomic ratio of In:Ga:Zn=1:1:1, the density of each of thenc-OS and the CAAC-OS is higher than or equal to 5.9 g/cm³ and lowerthan 6.3 g/cm³.

Note that there is a possibility that an oxide semiconductor having acertain composition cannot exist in a single crystal structure. In thatcase, single crystal oxide semiconductors with different compositionsare combined at an adequate ratio, which makes it possible to calculatedensity equivalent to that of a single crystal oxide semiconductor withthe desired composition. The density of a single crystal oxidesemiconductor having the desired composition can be calculated using aweighted average according to the combination ratio of the singlecrystal oxide semiconductors with different compositions. Note that itis preferable to use as few kinds of single crystal oxide semiconductorsas possible to calculate the density.

As described above, oxide semiconductors have various structures andvarious properties. Note that an oxide semiconductor may be a stackedlayer including two or more films of an amorphous oxide semiconductor,an a-like OS, an nc-OS, and a CAAC-OS, for example.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 8

A semiconductor device of one embodiment of the present invention can beused for display devices, personal computers, and image reproducingdevices provided with recording media (typically, devices that reproducethe content of recording media such as digital versatile discs (DVD) andhave displays for displaying the reproduced images). Other than theabove, as an electronic device which can be provided with thesemiconductor device of an embodiment of the present invention, mobilephones, game consoles including portable game consoles, portableinformation terminals, e-book readers, cameras such as video cameras anddigital still cameras, goggle-type displays (head mounted displays),navigation systems, audio reproducing devices (e.g., car audio systemsand digital audio players), copiers, facsimiles, printers, multifunctionprinters, automated teller machines (ATM), vending machines, medicalequipment, and the like can be given. FIGS. 18A to 18F illustratespecific examples of these electronic devices.

FIG. 18A illustrates a portable game console, which includes a housing5001, a housing 5002, a display portion 5003, a display portion 5004, amicrophone 5005, speakers 5006, operation keys 5007, a stylus 5008, andthe like. The semiconductor device of one embodiment of the presentinvention can be used for a variety of integrated circuits included inportable game consoles. Note that although the portable game consoleillustrated in FIG. 18A includes the two display portions 5003 and 5004,the number of display portions included in the portable game console isnot limited to two.

FIG. 18B illustrates a portable information terminal, which includes afirst housing 5601, a second housing 5602, a first display portion 5603,a second display portion 5604, a joint 5605, an operation key 5606, abiometric authentication device 5607, and the like. The semiconductordevice of one embodiment of the present invention can be used for avariety of integrated circuits included in portable informationterminals. The first display portion 5603 is provided in the firsthousing 5601, and the second display portion 5604 is provided in thesecond housing 5602. The first housing 5601 and the second housing 5602are connected to each other with the joint 5605, and the angle betweenthe first housing 5601 and the second housing 5602 can be changed withthe joint 5605. An image on the first display portion 5603 may beswitched depending on the angle between the first housing 5601 and thesecond housing 5602 at the joint 5605.

FIG. 18C illustrates a laptop personal computer, which includes ahousing 5401, a display portion 5402, a keyboard 5403, a pointing device5404, a biometric authentication device 5405, and the like. Thesemiconductor device of one embodiment of the present invention can beused for a variety of integrated circuits included in laptop personalcomputers.

FIG. 18D illustrates a hand mirror, which includes a first housing 5301,a second housing 5302, a mirror 5303, a joint 5304, a switch 5305, andthe like. The first housing 5301 and the second housing 5302 areconnected with the joint 5304, and the angle between the first housing5301 and the second housing 5302 can be changed with the joint 5304.Lighting devices are used for the first housing 5301 and the secondhousing 5302. The switch 5305 controls light, on/off, and the like ofthe lighting devices. The lighting device includes a planarlight-emitting element. This light-emitting element may have a structureof switching between the light-emission state and the non-light-emissionstate in accordance with the angle between the first housing 5301 andthe second housing 5302 at the joint 5304. The semiconductor device ofone embodiment of the present invention can be used for a variety ofintegrated circuits for controlling operation of the lighting device.

FIG. 18E illustrates a display device, which includes a housing 5701having a curved surface, a display portion 5702, and the like. Thesemiconductor device of one embodiment of the present invention can beused for a variety of integrated circuits for controlling operation ofthe display device used as the display portion 5702.

FIG. 18F illustrates a mobile phone, which includes a display portion5902, a microphone 5907, a speaker 5904, a camera 5903, an externalconnection port 5906, and an operation button 5905 in a housing 5901with a curved surface. The semiconductor device of one embodiment of thepresent invention can be used for a variety of integrated circuits forcontrolling operation of the display device used as the display portion5902.

Embodiment 9

FIG. 19 is a cross-sectional view of a liquid crystal display deviceintegrated with an active matrix touch sensor of one embodiment of thepresent invention. In FIG. 19 , a cross section a-a′ illustrates part ofa display element; b-b′, a sensor unit; and c-c′, part of circuit.

FIG. 19 illustrates an example in which the shape of the conductive film221 in FIG. 3 is modified. In FIG. 3 , the conductive film 221 is notprovided with a slit; while the conductive film 221 is provided with aslit in FIG. 19 . Since the structure of FIG. 19 is similar to that ofFIG. 3 except for the shape of the conductive film 221, the descriptionis omitted.

FIG. 20 is a cross-sectional view of a liquid crystal display deviceintegrated with an active matrix touch sensor of one embodiment of thepresent invention. In FIG. 20 , a cross section a-a′ illustrates part ofa display element; b-b′, a sensor unit; and c-c′, part of circuit.

FIG. 20 illustrates an example in which the conductive films 224 and 221in FIG. 3 are formed over the insulating film 218. FIG. 20 illustratesan example in which the conductive films 224 and 221 are formed over thesame surface.

A structure of a transistor used for the liquid crystal display deviceintegrated with the active matrix touch sensor of one embodiment of thepresent invention is not particularly limited and transistors withvarious structures can be used. Although the bottom-gate transistor isshown in this embodiment, this embodiment is not limited to this. Forexample, a top-gate transistor may be used.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

This application is based on Japanese Patent Application serial no.2014-243995 filed with Japan Patent Office on Dec. 2, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A display device having a display portioncomprising: a first substrate; a second substrate; and a liquid crystallayer provided between the first substrate and the second substrate,wherein the display portion includes a sensor unit and a first pixel,wherein the sensor unit includes a first capacitor comprising a firstelectrode and a second electrode, wherein the first electrode comprisesa first part of a first conductive film and the second electrodecomprises a second conductive film, wherein the first conductive filmfaces the second conductive film via the liquid crystal layer, whereinthe first pixel includes a transistor and a first pixel electrodeelectrically connected to the transistor, wherein the transistor, thefirst conductive film, and the first pixel electrode are providedbetween the first substrate and the liquid crystal layer, wherein thefirst conductive film is provided between the transistor and the firstpixel electrode, wherein the first part of the first conductive filmdoes not overlap with the first pixel electrode, and wherein a secondpart of the first conductive film has a region overlapped with the firstpixel electrode.
 2. The display device according to claim 1, wherein thetransistor comprises an oxide semiconductor film.
 3. The display deviceaccording to claim 1, wherein the first pixel electrode has a pluralityof silts.
 4. The display device according to claim 1, wherein the firstconductive film comprises a transparent conductive material.
 5. Thedisplay device according to claim 1, wherein the second conductive filmcomprises a transparent conductive material.
 6. The display deviceaccording to claim 1, wherein the display portion further comprises asecond pixel including a second pixel electrode, and wherein the sensorunit overlaps with the first pixel electrode and the second pixelelectrode.
 7. An electronic device comprising the display deviceaccording to claim
 1. 8. The display device according to claim 1,wherein the second part of the first conductive film is configured to bea common electrode.
 9. A display device having a display portioncomprising: a first substrate; a second substrate; and a liquid crystallayer provided between the first substrate and the second substrate,wherein the display portion includes a sensor unit and a first pixel,wherein the sensor unit includes a first capacitor comprising a firstelectrode and a second electrode, wherein the first electrode comprisesa first part of a first conductive film and the second electrodecomprises a second conductive film, wherein the first pixel includes atransistor and a first pixel electrode electrically connected to thetransistor, wherein the transistor, the first conductive film, and thefirst pixel electrode are provided between the first substrate and theliquid crystal layer, wherein the first conductive film is providedbetween the transistor and the first pixel electrode, wherein the firstpart of the first conductive film does not overlap with the first pixelelectrode, wherein a second part of the first conductive film has aregion overlapped with the first pixel electrode, and wherein the secondconductive film is provided over the first pixel electrode.
 10. Thedisplay device according to claim 9, wherein the transistor comprises anoxide semiconductor film.
 11. The display device according to claim 9,wherein the first pixel electrode has a plurality of silts.
 12. Thedisplay device according to claim 9, wherein the first conductive filmcomprises a transparent conductive material.
 13. The display deviceaccording to claim 9, wherein the second conductive film comprises atransparent conductive material.
 14. The display device according toclaim 9, wherein the display portion further comprises a second pixelincluding a second pixel electrode, and wherein the sensor unit overlapswith the first pixel electrode and the second pixel electrode.
 15. Anelectronic device comprising the display device according to claim 9.16. The display device according to claim 9, wherein the second part ofthe first conductive film is configured to be a common electrode.